Post on 24-May-2020
Accepted Manuscript
Periodical trends in [Co6E(CO)16]- clusters: Structural, synthetic and energy changesproduced by substitution of P with As
Roberto Della Pergola, Annalisa Sironi, Valentina Colombo, Luigi Garlaschelli,Stefano Racioppi, Angelo Sironi, Piero Macchi
PII: S0022-328X(17)30345-5
DOI: 10.1016/j.jorganchem.2017.05.041
Reference: JOM 19967
To appear in: Journal of Organometallic Chemistry
Received Date: 27 January 2017
Accepted Date: 18 May 2017
Please cite this article as: R. Della Pergola, A. Sironi, V. Colombo, L. Garlaschelli, S. Racioppi, A.Sironi, P. Macchi, Periodical trends in [Co6E(CO)16]- clusters: Structural, synthetic and energy changesproduced by substitution of P with As, Journal of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.05.041.
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Periodical trends in [Co6E(CO)16]- clusters: structural,
synthetic and energy changes produced by substitution of P
with As.*
By
Roberto Della Pergola,1,* Annalisa Sironi,1 Valentina Colombo,2 Luigi Garlaschelli,2 Stefano
Racioppi,2 Angelo Sironi,2,* Piero Macchi.3,*
1 Università di Milano-Bicocca- Dipartimento di Scienze Ambientali e della Terra, piazza della
Scienza 1 – 20126 Milano Italy
2 Università degli Studi di Milano – Dipartimento di Chimica– Via Golgi, 19 – 20133 Milano Italy.
3 University of Bern - Department of Chemistry and Biochemistry, Freiestrasse 3 - 3012 Bern -
Switzerland
roberto.dellapergola@unimib.it, angelo.sironi@unimi.it, piero.macchi@dcb.unibe.ch
ABSTRACT
The anionic cluster [Co6As(CO)16]- was synthesized through the reaction of Na[Co(CO)4] and
arsenic acid in THF at room temperature. Crystallization from MeOH/2-propanol yielded two
polymorphs that feature two slightly different isomers of the anion with the same PPh4+ cation. One
of the isomers is very similar to the known [Co6P(CO)16]-, formed by four edge fused triangles,
partially wrapping the main group atom. The other isomer features a deformed cage, which differs
mainly for a non-bonding Co-Co distance. The reasons for this unprecedented stereochemistry, and
the factors which may trigger this isomer, have been investigated by DFT calculations.
Keywords: Cobalt, Arsenic, Metal cluster, Solid state structure, DFT calculations
* Dedicated to Richard D. Adams for his outstanding contribution to Organometallic Chemistry
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Thanks to their tendency to catenation, the heavier elements of group V (As, Sb, Bi) are particularly
useful to construct molecular architectures, in combination with transition metals. The concern
about this chemistry reached its highest point in the ’80-’90 years, and scientists focused essentially
on structural aspects. Owing to this wide interest and this structural complexity, the field was
synthetically illustrated by Greenwood [1] and was thoroughly reviewed by Whitmire.[2]
Depending on the number of substituents (and the number of orbitals available for bonding), the
main group element may act simply as an exo-skeleton ligand, be a well-defined vertex of the
cluster skeleton, or occupy an interstitial position. Accordingly, AsR3 are typical ligands in
organometallic chemistry,[3] AsR fragments mimic M(CO)n moieties as vertices of the cage,[4] and
As atoms may be fully surrounded by metals in clusters like [Rh10As(CO)22]3-.[5] Transition and
main group elements may play interchangeable roles, as shown by the complete series As4-
n{Co(CO)3} n (n = 0,[6] 1,[7] 2,[8] 3 ,[9] 4[10]), which nicely illustrate the isolobal principle.[11]
Moreover, the construction of molecular architectures with different structural elements can be
relevant for catalysis, since the formation of strong E-M bonds can confer extra stability to the
molecules.[2] Accordingly, the quoted [Rh10As(CO)22]3- was self-assembled in conditions suitable
for the homogeneous catalytic conversion of CO-H2 mixtures into oxygenated compounds, and
proved to be stable at partial pressures of CO as high as 260 atm.[5] More recently, this class of
compounds has been used as single source for the preparation of binary and ternary phases
which,[12] on turn, can find application for magnetic nanoparticles,[13] for the deposition of thin
films [14] or for electrocatalysis.[15] In the latter field, the presence of the main group element
helps in forming amorphous layers which are more catalytically active than bulk metal. In particular
cobalt phosphides emerged as materials extremely active for both the hydrogen and oxygen
evolution reactions (HER and OER).[16] For all these reasons, we devoted our attention to the
synthesis of new Co-As clusters, trying to incorporate As atoms into small simple molecular
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first result in this field is the isolation of the anion [Co6As(CO)16]-, whose formula exactly matches
that of the corresponding [Co6P(CO)16]- phosphide,[17] but differs from it for several structural and
chemical aspects.
2 Results
2.1 Synthesis of [Co6As(CO)16]-
As(I) and As(III) compounds such as (AsPh)6 [4] or (AsMe)5, [7] AsCl3, [8] AsH3 [9] or AsPh3.[5]
are typically used as sources of As. Conversely, we used PCl5 as a source of P atoms in molecular
cobalt clusters.[18] Since arsenic pentahalide are unstable and not commercially available, we
tested the condensation of arsenic acid, (the hydrated As2O5·2H2O) with the sodium salt of
[Co(CO)4]-. The reaction in THF at room temperature is smooth, as clearly evidenced by the
darkening of the reaction mixture and the CO evolution. After about 1 day of stirring, the infrared
spectrum of the reaction mixture shows the presence of new carbonyl compounds, together with
some unreacted [Co(CO)4]-. When the As/Co molar ratio is lower than 1, the most intense bands are
located at 2025, 2011 and 1808 cm-1, assignable to the anion [Co6As(CO)16]-; minor bands at higher
wavenumbers denote the presence of neutral clusters, possibly the trimer As3Co9(CO)24.[9]
Conversely, if the As/Co molar ratio is increased to about 2, different uncharacterized species are
formed, presumably richer in As and similar to the known [Co4Sb2(CO)11]2- [19] and
[Co4Bi2(CO)11]2- anions.[20] Neutral and anionic species can be easily separated, by extracting the
former with hydrocarbon solvents. After repeated washing with hexane, the salt Na[Co6As(CO)16]
is left behind. It can be dissolved in methanol, and layered with a dilute solution of PPh4Cl in 2-
propanol. Diffusion of the two solutions allows crystal growth. Alternatively, the compound can be
isolated by precipitation with an ammonium or phosphonium salt, and used for further studies.
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-, in different solvents
and at different temperatures.
2.2 Solid state structure
The samples obtained from methanol (method 3.2.1 in the experimental) contained crystals
featuring two different morphologies (larger oblique prisms or smaller irregular chunks) both
affording reasonable X-ray diffraction patterns (though, of different quality). Conventional single-
crystal X-ray diffraction analysis afforded a full structural characterization of both species. They
resulted to be two conformational polymorphs of the [Co6As(CO)16][PPh4] salt (hereinafter, α-
1[PPh4] and β-1[PPh4]). In fact, the two structures differ not only in the packing of the cationic and
anionic moieties in the crystal (they feature, in fact, different space group types and lattice
parameters) but also in the stereochemistry of the anionic cluster units (1a in α-1[PPh4] and 1b in β-
1[PPh4], respectively). Actually, 1a and 1b are constitutional isomers rather than conformers, given
the presence or the absence of a weak Co-Co bond (vide infra). Thus, strictly speaking, the term
‘conformational polymorphs’ could be questionable here. However, we find this terminology
substantially correct because 1a and 1b easily interconvert in solution (vide infra) and, more
generally, metal carbonyl clusters often display ligands (and even metal-cage) fluxionalities in
solution.[21]
α-1[PPh4], which crystallizes in the monoclinic space group P21/c, has a significantly higher density
(1.812 vs. 1.758 g/cm3) and a better crystallinity than β-1[PPh4], which crystallizes in the
orthorhombic Pbca space group. As a matter of facts, eight small ‘cavities’ (each of ca. 10 Å3) can
be computed in β-1[PPh4]. However, they are too small to host solvent molecules and, within the
limits due to poor sample diffraction, do not contain any residual electron density. Thus, the
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to the slightly different molecular geometries of 1a and 1b.
α-1[PPh4] is isomorphous to the known [Co6P(CO)16][PPh4] salt [17a]; accordingly, the
stereochemistry of 1a resembles that of [Co6P(CO)16]- (hereinafter, 2) but for the differences
inherent to the larger semi-interstitial atom (As vs. P). Thus, one may describe the anionic cluster
cage as a folded chain of four edge-sharing triangles surrounding a “semi-interstitial” arsenic atom
(see the folding angles Table 1). The anions are close to the idealized C2 symmetry, with the two-
fold axis passing through the heteroatom and the middle of the Co1-Co2 edge. However, the metal
cage has an approximate C2v symmetry. Accordingly, the Co-E bonds belong to two classes: the
bonds to Co5 and Co6 atoms are significantly shorter than the other four. The Co-Co interactions
can be divided into three classes: the four edges involving the external Co5 and Co6 atoms, the four
shorter edges involving the central quadrilateral and the very long Col-Co2 edge, (see Table 1). All
Co-Co bond distances are comparable to those found in many cobalt carbonyl clusters but the very
long Col-Co2 interactions. Of the sixteen CO groups, fourteen are terminal and two symmetric
edge-bridging. The cobalt atoms Co5 and Co6 bear three terminal carbonyls, whereas each of the
other metal atoms is connected to one edge-bridging and to two terminal carbonyls.
The main difference between 1b and 1a concerns atoms Co1 and Co2 (see Figure 1 for a
comparison between the two geometries). In fact, in 1b the weak Co1-Co2 bond has an even longer
distance, exceeding the limit to classify it as a bond. This elongation implies a rotation of ca. 20°
about the pseudo three-fold axis of the Co(CO)3 moieties of Co1 and Co2. Quite evident is
especially the different orientation of the C15 and C16 carbonyls, bridging Co1-Co3 and Co2-Co4
bonds respectively (see Figure 1). This rearrangement preserves the overall C2 symmetry of the
anion but lowers (from C2v to C2) that of the cage.
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Figure 1: The overlay between structures 1a (red) and 1b (blue) as obtained from the corresponding αααα-1 and ββββ-1 salts. Note in particular the longer Co1-Co2 contact in 1b and the rotation of Co(CO)3 moieties for Co1 and Co2. The root mean square deviation between the two geometries is 0.6 Å.
Figure 2: The isomer 2a, 2b and the transition state TS2, from M06/6-311+G(d,p) calculations.
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Table 1. Selected bond distance and angles of isomers 1a, 1b, 2a, 2b and of the transition states TS1 and TS2 for [Co6X(CO)16]- (X = As, P) from
X-ray diffraction or from theoretical calculations (M06/6-311+G(d,p)). The theoretical calculations are in C2 symmetry.
E = P E= As
Expt. Theor. Expt. Theor. Expt.
2a[17a] 2a TS2 2b 1a 1a TS1 1b 1b
Selected Co-Co averaged distances
Co1-Co2 2.935 2.801 3.150 3.487 2.944 2.800 3.045 3.489 3.457
Co5-Co(1,3), Co6-Co(2,4) 2.664 2.646
2.673 2.680
2.628 2.644
2.602 2.623
2.720 2.703
2.724 2.728
2.678 2.687
2.634 2.658
2.660 2,672
Co1-Co(3,4), Co2-Co(3,4) 2.574 2.575
2.670 2.570
2.660 2.555
2.631 2.538
2.607 2.595
2.695 2.564
2.682 2.564
2.671 2.544
2.636 2.579
Co5-Co6 4.105 4.153 4.107 4.092 4.385 4.441 4.436 4.408 4.364
Selected E-Co (E = P, As) averaged distances
E-Co(1,2,3,4) 2.263 2.255 2.274 2.287 2.371 2.378 2.392 2.400 2.390
E-Co(5,6) 2.170 2.193 2.181 2.181 2.265 2.283 2.281 2.279 2.266
Dihedral angles (°) between edge sharing triangles
Co(1,2,3)/Co(1,2,4) 143.4 135.4 145.3 159.9 145,0 137.5 144.2 159.3 159.7
Co(1,2,3)/Co(1,3,5) 122.9 123.8 120.1 115.4 125.1 126.0 124.3 118.9 119.1
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Co(1,2,4)/Co(2,4,6) 122.0 123.8 120.1 115.4 124.3 126.0 124.3 118.9 118.4
Dihedral angles (°) between E, Co1,Co3 plane and carbonyls
E,Co(1,3),C(1) 105.7 112.3 112.4 88.9 105.0 111.1 109.6 87.7 85.2
E,Co(1,3),C(2) -156.9 -148.7 -151.7 -176.1 -159.2 -152.2 -155.0 -176.5 -179.5
E,Co(1,3),C(15) -64.8 -36.7 -63.1 -84.4 -69.8 -46.6 -64.4 -86.0 -86.7
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We have simulated the structures of anions 1a and 1b, as well as of the already known 2a and of the
not yet isolated 2b. Moreover, we searched for energy pathways interconnecting the isomers and
found the transition states TS1 and TS2. All geometry optimizations and frequency calculations
were performed using density functional theory (DFT) (see experimental section for more details).
The calculated geometries of 1a, 1b and 2a are in good qualitative and quantitative agreement with
the experimental results (Table 1). Co1-Co2 distance is not very sensitive to the change of semi-
interstitial atom, in fact 1a/2a and 1b/2b show similar lengths. Compared with X-ray data, the gas
phase DFT calculations underestimate the Co1-Co2 distance in anions a, which further confirms the
flexibility of this bond, very likely sensitive to the data collection conditions (such as P or T) when
determined in the solid state. We tested also the possible role of the dielectric medium surrounding
the anion and therefore optimized the geometries in various polarizable continuum model (PCM)
[22], simulating solvents with different dielectric constant. However, this variable did not affect
much the computed molecular geometries. The computed transition states show that the Co1-Co2
distance is in fact intermediate between 2a and 2b for the phosphide, whereas it results closer to 1a
for the arsenide. The bond distances and angles confirm that TS1 is an early transition state (see
Scheme 1). In Table 2, we report energy differences between isomers a and b. ∆E is the electronic
energy difference which is independent from the medium (in vacuo or PCM returns the same
value). From frequency calculations, we derived the corresponding enthalpies and Gibbs free
energy differences (∆H, ∆G), using thermal corrections at 1 atm and 298 K. ∆GPCM represents the
difference between free energy of solvation in THF obtained through PCM.
Table 2. The energy differences between isomers a and b for both 1 and 2. Results are in kcal/mol
E ∆E ∆H ∆G
∆GPCM
As 4.9 4.8 2.4 5.1 P 2.8 2.6 0.1 2.9
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driving force is certainly more pronounced for the As-derivative, whereas the Gibbs free energy
difference (in pure gas phase) is negligible for the P-derivative.
We also analyzed the potential energy surface of these clusters. We carried out linear transit
calculations in vacuo, by constraining various values of the Co1-Co2 distance, and computed the
local transition states (TS) using the Synchronous Transit-Guided Quasi-Newton method [23]. Only
TS2 features a single imaginary frequency, corresponding to the stretching of Co1-Co2, whereas
TS1 shows an additional negative, albeit small, eigenvalue (-10.4 cm-1), which corresponds to a real
frequency in TS2. The discrepancy between anions 1 and 2 is probably due to the size of the
integration grid, as for example observed by Ding and co-workers [24]. The overall reaction paths
can be summarized as in scheme 1.
Scheme 1. Calculated energy [kcal/mol] pathway for isomerization.
Here we note that the early transition state of 1 implies a much smaller barrier ∆E(TS1, 1a) compared
with ∆E(TS2, 2a).
From these data, we conclude that: 1) in both cases, the isomer with the longest Co1-Co2 bond is
the most stable, but the reaction equilibrium in the As derivative is certainly more shifted towards
the “open” isomer 1b (of course, this preference is fully consistent with the larger atomic radius of
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5
0
1
2
3
4
5
6
7
2.8
4.94.7
5.6
0
TS2
TS1
2a
1a
1b2b
∆E k
cal/m
ol
Co1-Co2 [Å]
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high and one should expect both species to be present in solution.
These conclusions should be merged with what previously observed on the crystal structure of the
two isomers: isomers a, although less stable in isolation, are better stabilized by packing forces that
counterbalance the unfavorable form of the cluster in polymorphs α . This may explain the reason
why isomers a are always observed for both As and P, although being only the kinetic products.
The calculated ∆E and ∆G may, in part, explain the reason why isomer b has not been isolated (yet)
for the P derivative. In fact, the thermodynamic driving force toward 2b is weaker than for 1b and a
higher kinetic barrier is present. Nevertheless, it is sensible to anticipate that an isomer of type 2b
should exist and could be in principle isolated.
3 Experimental
All the solvents were purified and dried by conventional methods and stored under nitrogen. All the
reactions were carried out under oxygen-free nitrogen atmosphere using the Schlenk-tube
technique.[25] Infrared spectra in solution were recorded on a Nicolet iS10 spectrophotometer,
using calcium fluoride cells previously purged with N2. A batch of Na[Co(CO)4] was prepared by
dissolving 20 g of Co2(CO)8 in anhydrous THF (50 mL), and allowing it to react with small pieces
of Na, until the IR bands of the reactant disappeared (2-3 days). The pale solution was filtered, and
the THF was dried in vacuum, under moderate heating, to remove all traces of solvent.
ν(CO) in THF : 2010vw, 1887vs, 1857 m cm-1
3.1 Synthesis of Na[Co6As(CO)16]
Na[Co(CO)4] (960 mg, 4.4 mmol) and As2O5·xH2O (480mg; 1.75 mmol) were suspended in THF
(25 mL) and stirred at room temperature. A brown solution was formed, and some CO evolution
was observed. After 1 day of stirring, the solution was filtered and the solvent was partially
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concentrated, until most of the product precipitated. The suspended solid was collected by filtration,
washed with 10 mL of heptane, and dried.
ν(CO) in MeOH : 2075vw, 2027vs, 2014s, 1975w, 1809 m cm-1 (Figure 3)
3.2 Synthesis of (PPh4)[Co6As(CO)16]
3.2.1 The crystals used for X-ray diffraction were obtained dissolving Na[Co6As(CO)16], obtained
as above, in the minimum amount of Methanol, and layering with a solution of PPh4Cl in 2-
propanol (ca. 0.5 mg/mL). After diffusion was completed, the mother liquors were eliminated by
syringe. The solid residue was washed with 2-propanol and dried.
3.2.2 To obtain larger amounts of compound, Na[Co6As(CO)16] was dissolved in Methanol and
treated with a concentrated solution of PPh4Cl in 2-propanol. After complete precipitation occurred,
the solid was collected by filtration, washed with 2-propanol and dried.
Typical yields 45-50% (calculated on Co).
Calc for C40H20AsCo6O16P C 39.51 ; H 1.66 %; found C 39.7 ; H 1.4 %.
ν(CO) in THF : 2074vw, 2027vs, 2012s, 1975w, 1954w, 1809 m cm-1 (figure 3)
3.3 X-ray Single Crystal Structure Determinations.
3.3.1 Intensity measurements. An oblique prismatic crystal of compound (α-1[PPh4]) of dimensions
0.33 × 0.18 × 0.17 mm and a irregular-shaped crystal of compound (β-1[PPh4]) of dimensions 0.13
× 0.12 × 0.12 mm, both mounted on glass fibers in the air, were transferred to an Enraf-Nonius
CAD4 automated diffractometer. Graphite-monochromated Mo-Kα, radiation was used. In both
cases the setting angles of 25 random reflections (16 < 2θ < 22°) were used to determine by least-
squares fit accurate cell constants and orientation matrices. The two data collections were
performed by the ω-scan method, within the limits 3 < 2θ < 25°, using a variable scan speed (from
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1[PPh4])], with a 25% extension at each end for background determination. Reflections
corresponding to the ±h, +k, +l and +h, +k, +l indices were collected for compounds (α-1[PPh4])
and (β-1[PPh4]), respectively. The total numbers of reflections measured were 7788 (α-1[PPh4]) and
7946 (β-1[PPh4]). Three standard reflections were measured every 3 h and no significant crystal
decay was observed in both data collections. The intensities were corrected for Lorentz and
polarization effects. An empirical absorption correction was applied in both cases based on ψ scans
[26] (ψ 0-360° every 10°) of suitable reflections with χ values close to 90°; the maximum,
minimum, and average relative transmission values were 1.00, 0.55, and 0.84 for complex (α-
1[PPh4]) and 1.00, 0.72, and 0.85 for (β-1[PPh4]), respectively. Two sets of 3 897 (α-1[PPh4]) and 2
168 (β-1[PPh4]) independent significant reflections, with I >3 σ(I), were used in the structure
solutions and refinements.
3.3.2 Structure solutions and refinements. Both structures were solved by direct methods
(SHELXS)
The refinements were carried out by full-matrix least-squares methods using SHELXL-2014/7.[27]
Anisotropic thermal parameters were assigned only to phosphorous and the anionic atoms.
Phenyls have been treated as rigid bodies with hydrogen atoms riding on their carbon atoms on
idealized positions.
Final Fourier difference maps showed residual peaks not exceeding ca. 0.8 e/ A-3. The final values
of the conventional agreement indices R1 and wR2 [I > 2σ(I)] were 0.0414 and 0.0828 for compound
α-1[PPh4] and 0.0483 and 0.0923 for compound β-1[PPh4], respectively.
The final positional parameters are listed in Tables 4 and 5 for α-1[PPh4] and β-1[PPh4],
respectively.
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Figure 3 – The IR spectra of Na[Co6As(CO)16] in MeOH (left) and PPh4[Co6As(CO)16] in THF
(right)
3.4. Computational details
All the calculations were performed with GAUSSIAN 09 package [28]. Initial structures of 1a, 1b
and 2a were taken from single crystal X-ray diffraction results. Full geometry optimizations of the
isomers were carried out considering C2 point group, followed by frequency calculation to confirm
the nature of the minima and to obtain thermochemical data. The functional M06[29] was chosen
with 6-311+G(d,p) basis for all the atoms. The same level of theory (M06/6-311+G(d,p)) was used
for both geometry optimizations and frequencies calculations. Solvent effect was accounted for
subsequent geometry optimizations using the Polarizable Continuum Model (PCM) [22]. A
standard cavity was used, and the dielectric constant of tetrahydrofuran (THF) was 7.4257, and the
initial structures were taken from the optimizations in gas phase. Cartesian coordinates
corresponding to all structures are given in the Supporting Information.
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1647
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975
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Co6As in THF
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4 Conclusions
The reaction between Na[Co(CO)4] and arsenic acid yields [Co6As(CO)16]-, which is the first
known anionic Co-As derivative, and other uncharacterized species. [Co6As(CO)16]- and
[Co6P(CO)16]- share a quite similar geometry, however we observed for the As derivative an
additional isomer (featuring one absent Co-Co bond), not yet known for the P-substituted species.
Theoretical calculations predict for both species that the larger cage is the more stable isomer,
although the experimentally observed packing for this species is much less efficient, which may
explain its more elusive behaviour.
The conversion of [Co6As(CO)16]- into larger clusters, possibly with interstitial As atoms will be
explored, as a step toward new Co-As materials. Moreover, we plan to carry out thorough
characterizations of the electron density distributions in both isomers.
Acknowledgements
This work was supported by University of Milano Bicocca (RDP, AS).
PM and SR thank the Swiss National Science Foundation (project 160157) for financial support.
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Identification code α-1[PPh4] β-1[PPh4] Empirical formula C40 H20 As Co6 O16 P C40 H20 As Co6 O16 P Formula weight 1216.03 1216.03 Temperature 298(2) K 298(2) K Wavelength 0.71073 A 0.71073 A Crystal system Monoclinic Orthorhombic Space group P 21/c P b c a a/Å 10.082(3) 21.191(5) b/Å 21.266(5) 20.370(5) c/Å 20.791(5) 21.284(5) α/° 90.0 90.0 β/° 91.05(2) 90.0 γ/° 90.0 90.0 V/Å3 4457(3) 9187(4) Z, Calculated density /Mg m-3 4, 1.812 8, 1.758 Absorption coefficient /mm-1 3.023 2.933 F(000) 2392 4784 Crystal size /mm 0.33 × 0.18 × 0.17 0.13 × 0.12 × 0.12 θ-range/° 2.998 to 24.974 3.189 to 24.898 Limiting indices -11≤ h ≤11, 0≤ k ≤25, 0≤ l ≤24 0≤ h ≤25, 0≤ k ≤24, 0≤ l ≤25 Reflections collected/unique 7788 / 7788 7946 / 7946 Completeness to θ-max 99.8 % 99.4 % Absorption correction Psi-scan Max. and min. transmission 1.0 and 0.78 1.00 and 0.91 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7788 / 0 / 409 7946 / 0 / 409 Goodness-of-fit (F2) 0.995 0.902 R1, wR2 [I > 2σ(I)] 0.0414, 0.0828 0.0483, 0.0923 R1, wR2 (all data) 0.1476, 0.1010 0.2961, 0.1329 Largest diff. peak and hole/e Å-3 0.705, -0.504 0.804, -1.024
† Electronic Supplementary Information (ESI) available: CCDC…… (1a) and CCDC …… (1b) contains the supplementary crystallographic data for compounds α-1[PPh4] and β-1[PPh4]. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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ACCEPTED MANUSCRIPT Table 4. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (A2x 103) for α-1[PPh4]. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
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Co(1) 9810(1) 2567(1) 9671(1) 46(1) Co(2) 10899(1) 3140(1) 10857(1) 50(1) Co(3) 9387(1) 3727(1) 10020(1) 50(1) Co(4) 10162(1) 1980(1) 10760(1) 45(1) Co(5) 7269(1) 2985(1) 9770(1) 47(1) Co(6) 9064(1) 2698(1) 11684(1) 54(1) C(1) 9075(7) 2142(3) 9031(3) 64(2) O(1) 8655(6) 1841(3) 8615(3) 103(2) C(2) 11006(8) 2998(3) 9257(3) 73(2) O(2) 11865(6) 3214(3) 8975(3) 105(2) C(3) 12497(8) 2832(3) 10717(4) 70(2) O(3) 13549(5) 2661(3) 10624(3) 99(2) C(4) 11168(7) 3532(4) 11584(4) 74(2) O(4) 11470(5) 3819(3) 12021(3) 115(2) C(5) 9493(8) 4169(3) 9288(4) 75(2) O(5) 9561(7) 4467(3) 8836(3) 126(3) C(6) 8578(7) 4288(3) 10515(4) 71(2) O(6) 8071(6) 4630(3) 10847(3) 113(2) C(7) 11493(7) 1659(3) 11235(3) 62(2) O(7) 12305(5) 1435(3) 11545(3) 91(2) C(8) 9039(7) 1332(3) 10682(3) 62(2) O(8) 8335(6) 924(3) 10612(3) 100(2) C(9) 7322(7) 3262(3) 8951(4) 60(2) O(9) 7315(6) 3418(3) 8430(2) 92(2) C(10) 6403(7) 2250(3) 9746(3) 60(2) O(10) 5848(6) 1790(3) 9741(3) 108(2) C(11) 6103(7) 3498(3) 10140(3) 61(2) O(11) 5382(5) 3822(3) 10385(3) 92(2) C(12) 10254(8) 2414(4) 12264(3) 83(2) O(12) 10970(6) 2238(4) 12653(3) 137(3) C(13) 7793(8) 2117(4) 11783(3) 65(2) O(13) 6974(6) 1755(3) 11839(3) 94(2) C(14) 8363(6) 3399(4) 12035(3) 64(2) O(14) 7929(6) 3831(3) 12263(3) 95(2) C(15) 10921(7) 1881(3) 9930(3) 58(2) O(15) 11711(5) 1559(3) 9692(2) 90(2) C(16) 11115(7) 3898(3) 10368(3) 59(2) O(16) 11921(5) 4287(2) 10318(3) 92(2) As 8678(1) 2837(1) 10614(1) 38(1) P 5812(2) -383(1) 12095(1) 42(1) C(111) 5652(4) -1219(2) 12185(2) 47(2) C(112) 5862(4) -1605(2) 11657(2) 66(2) C(113) 5775(5) -2254(2) 11721(2) 84(2) C(114) 5477(5) -2518(2) 12312(2) 88(2) C(115) 5266(4) -2132(2) 12841(2) 83(2) C(116) 5353(4) -1483(2) 12777(2) 63(2)
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ACCEPTED MANUSCRIPT C(121) 7509(3) -170(2) 11986(2) 41(1) C(122) 8059(4) 342(2) 12310(2) 56(2) C(123) 9390(4) 491(2) 12234(2) 73(2) C(124) 10171(3) 127(2) 11834(2) 75(2) C(125) 9621(4) -384(2) 11510(2) 88(2) C(126) 8290(4) -533(2) 11586(2) 67(2) C(131) 4832(3) -149(2) 11410(2) 46(2) C(132) 5152(3) 396(2) 11079(2) 62(2) C(133) 4345(4) 601(2) 10571(2) 78(2) C(134) 3219(4) 261(2) 10396(2) 69(2) C(135) 2899(3) -285(2) 10728(2) 63(2) C(136) 3706(4) -489(2) 11235(2) 55(2) C(141) 5227(4) 13(2) 12792(2) 45(2) C(142) 5874(3) -55(2) 13383(2) 53(2) C(143) 5388(4) 247(2) 13923(2) 64(2) C(144) 4255(4) 617(2) 13871(2) 74(2) C(145) 3607(3) 685(2) 13280(2) 78(2) C(146) 4093(4) 383(2) 12740(2) 63(2)
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ACCEPTED MANUSCRIPT Table 5. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (A2 x 103) for β-1[PPh4]. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
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Atom x y z U(eq) ________________________________________________________________
Co(1) -915(1) 617(1) 2579(1) 45(1) Co(2) 16(1) -776(1) 2543(1) 48(1) Co(3) -262(1) 105(1) 1679(1) 45(1) Co(4) -370(1) -75(1) 3474(1) 45(1) Co(5) 9(1) 1318(1) 2079(1) 51(1) Co(6) 869(1) -179(1) 3270(1) 56(1) As 209(1) 392(1) 2639(1) 42(1) C(1) -1542(5) 535(5) 2044(5) 66(3) O(1) -1990(4) 511(5) 1745(4) 116(3) C(2) -1187(4) 1318(5) 3007(5) 55(3) O(2) -1383(4) 1756(4) 3275(4) 84(3) C(3) -371(5) -1398(5) 2965(5) 58(3) O(3) -629(4) -1847(4) 3185(4) 100(3) C(4) 603(5) -1274(5) 2157(5) 56(3) O(4) 983(4) -1588(4) 1927(4) 111(3) C(5) 441(5) -70(5) 1250(5) 61(3) O(5) 900(4) -170(4) 979(4) 91(3) C(6) -764(5) 253(5) 1020(5) 58(3) O(6) -1045(4) 338(4) 582(3) 85(3) C(7) -528(5) -682(6) 4072(5) 64(3) O(7) -641(4) -1028(4) 4464(4) 103(3) C(8) -349(5) 614(6) 3999(5) 72(3) O(8) -339(5) 1043(4) 4334(4) 116(3) C(9) 81(5) 1920(5) 2685(5) 56(3) O(9) 117(4) 2305(4) 3079(4) 87(3) C(10) -601(5) 1623(5) 1572(5) 62(3) O(10) -976(4) 1830(4) 1241(4) 97(3) C(11) 714(5) 1405(5) 1650(5) 62(3) O(11) 1172(4) 1487(4) 1366(4) 96(3) C(12) 1534(5) -279(6) 2783(6) 90(4) O(12) 1966(4) -357(6) 2466(5) 157(5) C(13) 841(5) -912(6) 3733(6) 78(4) O(13) 864(4) -1375(4) 4037(5) 118(3) C(14) 1109(5) 452(6) 3807(6) 76(4) O(14) 1271(4) 862(4) 4126(4) 112(3) C(15) -1209(4) -38(5) 3154(4) 48(3) O(15) -1698(3) -294(3) 3253(3) 69(2) C(16) -572(5) -772(5) 1868(5) 55(3) O(16) -965(3) -1121(3) 1657(3) 76(2) P 1942(1) 2865(1) 4616(1) 45(1) C(111) 2202(3) 2212(3) 5108(3) 50(3) C(112) 2703(3) 1815(3) 4925(2) 63(3) C(113) 2942(2) 1347(3) 5337(3) 72(3)
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ACCEPTED MANUSCRIPT C(114) 2680(3) 1276(3) 5932(3) 62(3) C(115) 2179(3) 1673(3) 6115(2) 68(3) C(116) 1940(2) 2141(3) 5703(3) 60(3) C(121) 2351(3) 3605(3) 4808(3) 46(3) C(122) 2323(3) 4134(3) 4396(2) 61(3) C(123) 2603(3) 4728(3) 4557(3) 73(3) C(124) 2911(3) 4793(3) 5130(3) 86(4) C(125) 2939(3) 4264(4) 5542(3) 95(4) C(126) 2659(3) 3671(3) 5381(3) 77(4) C(131) 2100(3) 2677(3) 3817(3) 46(3) C(132) 2695(3) 2801(3) 3570(3) 82(4) C(133) 2832(3) 2627(4) 2954(4) 98(4) C(134) 2374(4) 2328(4) 2584(3) 105(4) C(135) 1778(4) 2204(4) 2831(4) 133(6) C(136) 1641(3) 2378(4) 3448(4) 98(4) C(141) 1114(2) 2984(3) 4750(3) 48(3) C(142) 874(3) 3615(3) 4814(3) 50(3) C(143) 228(3) 3711(3) 4881(3) 70(3) C(144) -178(2) 3174(3) 4884(3) 72(3) C(145) 63(3) 2543(3) 4820(3) 84(4) C(146) 709(3) 2448(2) 4753(3) 67(3)
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ACCEPTED MANUSCRIPTHighlights
� The synthesis of a new Co-As cluster, namely [Co6As(CO)16]-, is reported.
� The cluster has composition and structure similar to the corresponding phosphide � Two isomers of the clusters were isolated in the solid state, differing for the number of Co-
Co bond � DFT studies have shown that the isomer with less Co-Co bond is the more stable, both for P
and As � The energy difference for the two isomers is more pronounced for As, in keeping with the
larger atomic dimensions � The less stable isomer is stabilized by more efficient crystal packing